1. Field of Invention
The subject invention relates to burners used for the combustion of liquid fuels, specifically to an improved burner design for accommodating the unique properties of high-viscosity and waste oil.
In the United States alone, an estimated 3 billion gallons of waste oil are generated annually. Disposal of this potentially hazardous substance is possible in a number of different ways. Perhaps the most environmentally sound and economically efficient method is by combustion for commercial or domestic heating purposes.
Much of the waste oil produced in the United States is attributable to small establishments (i.e., small automotive repair shops and garages, businesses specializing in automotive oil changes, etc.). Burning waste oil to provide space heat or hot water for such operations would be preferable to paying the high costs of proper disposal or transportation for reprocessing. Unfortunately, the cost of waste oil burners in terms of initial capital outlay, installation, operation, and maintenance is often prohibitive. In addition, serious questions remain as to the safety and reliability of some waste oil burners on the market today.
Due to the unique and variable properties of waste oil supplies, conventional furnace oil burners, with their standard safety features, are not effective in the combustion of waste oil. Waste oil possesses characteristics far different from conventional furnace fuels; waste oil is typically very high in viscosity and replete with incombustible contaminants making combustion difficult by usual means. In addition, waste oil supplies frequently vary in viscosity and contaminant level and on occasion a waste oil furnace owner may choose to burn furnace fuel rather than waste oil in a waste oil burner. Therefore, it is important that a waste oil burner be easily and effectively adjustable to accommodate fuels of varying composition and viscosity.
The present invention proposes a unique and simple burner design that, when used in conjunction with an emissions scrubber such as that disclosed by U.S. Pat. No. 5,041,274, Aug. 20, 1991, Kagi, will provide a safe, efficient, cost-effective, and environmentally sound method of waste oil disposal.
2. Discussion of Prior Art
Overview of Conventional Waste Oil Burner Structure and Manner of Operation. Most waste oil burners operate in a similar manner: waste oil is filtered of contaminants and preheated in order to reduce oil viscosity. Next, a gear-driven oil pump transports oil to the burner from a remote source. On reaching the burner, the oil is suctioned through a low-pressure, aspiration-type nozzle by a compressed air current in order to break up the oil flow into a fine mist as required for proper combustion. The process of breaking up the oil flow into microscopic droplets is called "atomization." The atomized oil is then ignited by constant-spark electrodes. A constant spark is required to initiate and maintain combustion. In addition, prior art waste oil burners typically require oil solenoid valves to stop the flow of pressurized fuel through the nozzle after the burner is shut down.
Once flame is established, the combustion rate must be monitored to avoid "over-firing" or "under-firing" the furnace. Over-firing occurs when the flame length approaches the back wall, or "target", of the combustion chamber. Flame length increases with combustion rate in most waste oil furnaces because the secondary air required for combustion is fed parallel to the oil flow. If the combustion chamber is allowed to overheat, an explosion of the unit is possible; therefore, most waste oil burners have a fairly limited firing capacity and are engineered to shut down in the event of over-firing.
Under-firing is a less serious condition, usually caused by an excessively viscous fuel supply and is characterized by a weak, erratic flame and low heat output.
While numerous patents have been issued for waste oil burners of acceptable operation, all waste oil burners heretofore known suffer from a number of disadvantages:
Oil Preheating Required. Oil must be atomized into microscopic droplets in order to create greater surface area and achieve a complete burn. Waste oil is very high in viscosity; therefore, most waste oil burners preheat the oil in order to lower the viscosity and obtain maximum atomization. Unfortunately, heating waste oil to high temperatures also causes oil carbonization or "sludging" which can clog nozzles, thereby reducing burner efficiency or rendering the burner inoperable. The cost of high-temperature preheating also detracts from the economic savings sought by most waste oil furnace owners.
Remote Oil Pump and Compressed Air Supply Required. Most contemporary waste oil burners use a remote, gear-driven oil pump to convey oil from its source to a low-pressure suction nozzle for atomization. Because modern oil pumps achieve average pressures of only 100 psi, a compressed air flow is used to aerodynamically siphon the oil through an aspiration-type nozzle. External pump and compressed air requirements are costly and complicate furnace installation, operation, and maintenance. In addition, the colloidal, abrasive contaminants present in waste oil, even after filtration, drastically shorten the working use span of conventional oil pumps which are expensive to replace.
Most Lack Oil Flow Rate Control. Waste oil supplies frequently vary in viscosity and contaminant level and on occasion a waste oil furnace owner may choose to burn furnace fuel rather than waste oil in a waste oil burner. Therefore, it is important that a waste oil burner be easily adjustable to accommodate fuels of varying composition and viscosity to avoid burner over or under-firing.
Many contemporary waste oil burners do not feature an effective method of oil flow regulation making said burners susceptible to under-firing or over-firing. An under-firing condition, characterized by a weak, irregular flame and low heat output, may result if the oil flow rate cannot be adjusted to accommodate extremely high viscosity oil. A more serious and potentially dangerous situation is presented by burner over-firing.
If the oil flow rate of a burner cannot be adjusted for low viscosity fuel, inadvertent over-firing is possible. When oil pressure remains constant, low-viscosity oil is capable of flowing at an increased rate through a nozzle for ignition. An elevated oil flow rate may lead to an elongated flame, an over-firing precursor, in burners that feed secondary combustion air parallel to the oil flow.
Burner over-firing causes the cabinet to overheat and can result in an uncontrolled fire or explosion. Over-firing can be a potential problem, and source of danger for any burner transporting pressurized oil to an output nozzle without a means of oil flow control.
Many waste oil burners on the market today can be inadvertently over-fired, creating a extremely hazardous situations, because such burners do not possess a means of oil flow regulation. As a safety precaution, such burners usually contain an automatic switch to shut down the burner in the event of overheating. A consequence of such safety precautions is to limit BTU output.
Combustion Rate Necessarily Limited to Avoid Over-Firing. Conventional waste oil burners address the risk of over-firing and its associated hazards by limiting heat output. Waste oil burner manufacturers generally install a temperature-sensitive switch that will automatically shut down the burner in the event of over-heating. BTU output is necessarily limited in such designs since an increase in combustion rate varies directly with flame length and heat output.
Therefore, in order to provide a wide variety of BTU output levels, waste oil furnace manufacturers must generally produce several different-sized furnace models; one standard size furnace of the typical design, lacking an effective method of fuel flow rate control, is not capable of providing a widely variable heat output.
Constant Spark Ignitors Required. Most waste oil burners require constant spark ignitors to keep the burner in a continuously firing method. Constant spark ignitors have a relatively short working use expectancy and add to the cost of operating and maintaining a waste oil burner.
Oil Solenoid Valves Required. Conventional waste oil burners also require the use of an oil solenoid valve to stop the flow of pressurized oil through the nozzle after the burner ceases operation. The leakage of oil into a "cold" combustion chamber can result in difficult ignition, a foul smell and profuse smoke upon later burner operation, and the creation of deposits in the burner chamber leading to irregularities in burner performance. Oil solenoid valves add to the cost of manufacturing waste oil burners and potentially increase the cost of maintenance.
Secondary Air is Fed Parallel to the Oil Flow. The secondary air required for combustion in most modern waste oil burners is fed parallel to the flame through a blast tube or other air conduit. Consequently, an increase in combustion rate leads directly to an increase in flame length. Flame length must be carefully monitored in such burner designs to avoid over-firing.